This invention relates to improvements in torsional vibration dampers of the type wherein two coaxial rotary components are turnable relative to each other against the opposition of one or more one-piece or composite coil springs. Torsional vibration dampers of such character can be utilized with advantage in the power trains of motor vehicles, e.g., they can constitute composite flywheel assemblies between the output shafts of prime movers (such as the crankshafts or camshafts of internal combustion engines) and the housings or pressure plates of friction clutches, or composite clutch discs (also called clutch plates) in the friction clutches which operate between the prime movers and the change-speed transmissions of motor vehicles.
A torsional vibration damper which embodies one or more features of the present invention is disclosed, for example, in published German patent application No. 199 12 970 A1. This publication discloses a damper wherein the means for yieldably opposing rotation of at least one component: of two coaxial rotary components comprises an elongated arcuate compression coil spring having two end coils or convolutions and a plurality of intermediate coils or convolutions (hereinafter, such constituents of the coil spring will be referred to as convolutions). The intermediate convolutions include a first set having first outer diameters and at least one additional set having different second outer diameters. The two coaxial rotary components of the torsional vibration damper embodying the just described coil spring are flywheels in the form of shells together forming a housing which defines an elongated arcuate chamber for the coil spring. Each shell has a retainer which is confined in the chamber, and each end convolution of the coil spring abuts a different one of the two retainers so that the spring opposes angular movements of the retainers toward each other but urges such retainers away from each other.
A drawback of the just described conventional torsional vibration damper is that, when the two components are driven to rotate jointly at a high speed, the intermediate convolutions of the coil spring move or tend to move radially outwardly under the action of centrifugal force and come into pronounced frictional engagement with the internal surfaces which surround the arcuate chamber being defined by the two components. Such frictional engagement between the intermediate convolutions of the coil spring and the adjacent portions of the two components is undesirable on several grounds. For example, the internal surfaces of the two components and the surfaces of the radially outermost portions of the intermediate convolutions of the coil spring undergo pronounced wear and generate heat which must be dissipated, often at a high cost involving time and/or material, e.g., due to the need for the use of expensive materials for the components and/or due to the need for the application of highly wear-resistant coatings or the like.
Reference may also be had to commonly owned U.S. Pat. No. 5,980,386 (granted Nov. 9, 1999 to Friedmann et al. and disclosing a torsional vibration damper between a rotary output element of a prime mover and a friction clutch), U.S. Pat. No. 5,759,106 (granted Jun. 2, 1998 to Reik et al. and disclosing a different torsional vibration damper between a rotary output element of an engine and the rotary input element of a friction clutch), U.S. Pat. No. 5,632,365 (granted May 27, 1997 to Maucher and disclosing a clutch disc embodying a torsional vibration damper between a set of friction linings (which are flanked by and receive torque from the pressure plate and the counterpressure plate of a friction clutch) and the input shaft of the change-speed transmission), as well as U.S. Pat. No. 5,161,660 (granted Nov. 10, 1992 to Huber and disclosing a clutch plate or clutch disc with several discrete coil springs operating between two constituents of torque transmitting means installed between the flywheels and the engine on the one hand, and the input element of the change-speed transmission on the other hand). The disclosure of each of the aforementioned U.S. patents is incorporated herein by reference.